544 
NATURE 
[Aprit 8, 1897 
the product of the concentrations of all three substances. 
Without making assumptions, the truth of which cannot at pre- 
sent be verified, it is impossible to represent the reaction by 
means of a chemical equation, in which the change takes place 
between three molecules only. Like many other reactions, it 
is of a lower order than would be the case if the order were de- 
termined by the number of molecules represent ed by the chemical 
equation as taking part in it. The cause of this simplicity 
remains at present unknown. The influence of temperature on 
the velocity of change is well represented by Van ’t Hoffs well- 
known equation (‘‘ Etudes,” p. 115). An increase of temper- 
ature from 0° to 10° C. increases the velocity 2°7 times ; all other 
reactions, so far studied, are influenced to much the same extent, 
the effect of a rise of temperature of 10° being to increase the 
velocity from 2 to 3°6 times; the average number is 2°8. 
THE additions to the Zoological Society’s Gardens during the 
past week include two Californian Quails (Cadl¢pepla caléfornica, 
é ?) from California, presented by Mr. T. M. Howells; a 
Black-headed Lemur (Lemur brunneus), a Madagascar Boa 
(Boa madagascariensis) from Madagascar, a Canarian Pigeon 
(Colunba laurtvora) from the Canary Islands, deposited; two 
Black-necked Storks (Xenorhynchus australis) from Malacca, 
two Larger Tree Ducks (Dendrocygna major) from India, a 
Ruddy Sheldrake (Zadorna casarca, 8), four Tufted Ducks 
(fuligula cristata), European, purchased. 
OUR ASTRONOMICAL COLUMN. 
Mr. Isaac ROBERTS ON LONG-EXPOSURE PHOTOGRAPHS. 
—In the current number of Avow/ledge, Mr. Isaac Roberts de- 
scribes a beautiful photograph of Orion, taken by him with an 
exposure of seven: hours thirty-five minutes, the photograph 
“‘depicting very probably the maximum of extent and detail 
that can be shown by aid of photographic methods.” This 
statement, coming from one so versed in celestial photography, 
cannot be considered lightly, but must be carefully weighed 
before judgment be given. The reasons which Dr. Roberts 
gives for this statement are as follows: (1) The film of the 
negative is, in consequence of prolonged exposure to the latent 
sky luminosity, darkened on development to a degree that would 
obscure faint nebulosity and faint stars. (2) Longer exposures 
of the plates would not reveal additional details of nebulosity, 
nor more faint star images. Dr. Roberts goes on to say that, 
although he has taken all precautions to protect the plates from 
extraneous light, to photograph only on clear evenings, c., 
yet the longer the exposure the darker the film becomes in the 
development of the images. The sequence, he states further, 
has been observed for many years on all very sensitive films 
which have had long exposure, and the results have been prac- 
tically invariable. An important point, favouring Dr. Roberts’ 
statement, is that the unexposed margins of the films do not 
undergo this process of being darkened, but remain perfectly 
clear. The point raised by him is one well worth consideration 
in these days of long exposures ; and although the evidence he 
brings together is strong, yet we hope he has not proved his 
case, 
VaNnapium IN SCANDINAVIAN RuTILE.—For producing 
the spectrum of titanium, Prof. B. Hasselberg used titanic acid 
in the form of rutile in the electric arc, finding that it was more 
suitable than commercial titanium. This rutile came from 
Kragerée, in Norway, its other chief component, besides titanic 
acid, being oxide of iron, in a quantity of about I or 2 per 
cent. The spectrum obtained from this substance, after the 
elimination of known impurities, was thought at first to be pure 
titanium, but it was found ‘‘that among the fainter and faintest 
lines of my titanium spectrum there are several that doubtless 
belong to vanadium.” A re-examination of a large piece of the 
latter, and subsequent comparison photographs of vanadium 
and rutile, exhibited many striking similarities. Another kind 
of rutile was put to the same test. This was Swedish rutile from 
Karingbricka, in Westmanland, which contained chromium in 
addition. A comparison photograph of the spectra showed 
hat the same series of coincidences was found as in the case of 
NO. 1432, VOL. 55] 
the Norwegian rutile, as Prof. Hasselberg shows in the table 
of his results, given in the Astrophysecal Journal for March (No. 
3). Further spectroscopic experiments suggested that the 
Swedish variety contained a greater amount of vanadium than 
the Norwegian ; but whether the difference is sufficient to be 
recognised, or determined quantitatively chemically, remains 
uncertain. 
CoLuMBIA UNIVERSITY OBSERVATORY’S PUBLICATIONS. 
—In the two numbers (10 and 11) of the Contributions of this 
Observatory, Prof. Harold Jacoby presents two communications 
on (1) the reduction of stellar photographs with special refer- 
ence to the Astro-photographic Catalogue plates, and (2) on the 
permanence of the Rutherfurd photographic plates. The first 
paper has been written at the request of Dr. Gill, who asked him 
to put together the formula which seemed best for the reduction 
of the Astro-photographic Catalogue plates. Prof. Jacoby ac- 
knowledges the work of others on the subject, and the method 
he gives is suitable for the reduction of any photographic 
plates, whether the programme of the Permanent Committee 
has been adopted or not. The only restrictions are that the 
centre of the plate must be more than 15° from the pole, and 
that the plate does not cover more than two square degrees. A 
description of the method would be too long to give here, so we 
will confine ourselves to the statement that Prof. Jacoby’s 
formule greatly facilitate the computation asa whole. As an 
illustration of the method of reduction, he gives a fully worked- 
out example of a plate taken at Paris in 1891, and discussed by 
M. Prosper Henry. The second communication, dealing with 
the permanence of the Rutherfurd plates, gives the results of a 
comparison of the old measures of the Pleiades and those quite 
recently completed. The object of the investigation was to test 
the durability of the photographic film, and see whether any 
deformation, either contraction or expansion, had occurred in 
the interval since the first measurement, made nearly a quarter of 
a century ago. The question is one of great importance, since 
some of Rutherfurd’s photographs are still unmeasured ; it has, 
further, a great bearing on the plates of the astro-photographic- 
chart of the heavens. The result of the investigation can be 
best illustrated by extracting from the final table the figures. 
representing the differences between the old and new measures 
as obtained from three separate plates. These are as. 
follows :— 
Rutherfurd Measures minus New Measures. 
Plate 16. Plate 18. Plate 22." 
Stars |77 ] ae 
Angle. | Dist Angle. Dist. Angle. Dist 
“ | “ a“ a“ “ “ 
A 34 ooo | —o'12 | —0°24 | —0'21 +007 |+0'26 
18m | — ‘06 | — ‘06 | + “12 | - *05 | — 08 | — “34 
AI2 - ‘or | — 18] £ “40 | + ‘14 | + *16] — “30 
A22 | — 04 | + °27 | — 06 | — ‘o8!) = *06}] + ‘19° 
A24 | — ‘02 | + ‘16 oo | + °30 — “13 | + ‘IO 
A28 | + ail = “Toseiers. |p “13, |, ee oes 
A 30 | — ‘02 ‘or | = “45 | + 08 | + “17 | = “OL 
A39 | + ‘41 | + 03 | + ‘14 | — ‘18 | + °39 | + ‘02 
The conclusions that can be drawn from the whole discussion. 
are that the positions of the individual stars on the plates may be 
practically determined from either set of measures, the mean, 
error amounting to about o”"1. Thus the new measures will 
furnish practically identical results with those that would have 
been obtained if the plates had been measured twenty years 
earlier. 
A GIFT TO THE PARIS ACADEMY OF 
SCIENCES. 
HE Paris correspondent of the Z?mes, writing under date- 
April 5, makes the following announcement :— 
M. Berthelot read this afternoon, at the Academy of Sciences,. 
the following letter addressed to him in French by Mr. H. Wilde,. 
